1. Field of the Invention
The present invention relates to a disk playing apparatus, and more particularly relates to a disk playing apparatus for playing the so-called CLV disk.
2. Description of Background Information
As the method for recording a signal along a track on a disk-shaped recording carrier, the constant angular velocity (CAV) mode and constant linear velocity (CLV) mode are generally used.
In the field of the optical video disk, there coexist CAV disks and CLV disks which are produced according the CAV and CLV modes respectively. On the other hand, only CLV disks exist in the case of digital audio disks. The advantage of the CAV disks is that the angular velocity of the rotation of the disk is constant independently of the position of an information reading point of the pickup. This means it is unnecessary to change the rotational speed of the disk even if the pickup is rapidly translated in a radial direction for searching particular address information, and the signal detection from the disk is performed in a stable manner simply by maintaining the rotation of the disk at a constant speed. Therefore, the CAV disks are suited for applications in which a high speed search operation is required. Furthermore, because it is unnecessary to change the rotational speed of the spindle motor for rotating the disk in relation to the search operation, the power source for driving the motor need not have a large capacity.
When a CLV disk is played, conversely, the normal speed of rotation of the disk changes depending on a relative position (referred to as radial position hereinafter) of the information reading point of the pickup in the radial direction of the disk. Therefore, it is necessary to use a spindle motor and a driving power source which can rapidly accelerate and decelerate the disk in uses in which the search operation is to be performed quickly. Furthermore, since the capability of the spindle motor to follow changes in the rotational speed is limited, a time period is required before the rotation of the spindle motor becomes stable at a desired linear velocity. This has been imposing a limitation to raise the speed of the search operation. In addition, if the search operation is performed frequently, the electric power supplied to the spindle motor becomes several times higher than the normal value. This in turn results in problems of the generation of heat and vibrations caused by torque variations, and measures must be taken to eliminate such problems.
However, with CLV disks, there is an advantage that the recording area of the disk which cannot be increased is efficiently used. Specifically, information can be recorded on a CLV disk twice as much as information recordable on a CAV disk.
The CLV recording method is used in CD-ROM disks and CD-I disks which have the same format as the digital audio disk. Therefore, the problems peculiar to the CLV disk are also experienced when data is retrieved by searching information recorded on a data disk of these kinds. For constructing a system providing large amount of information requiring a plurality of disks, it is necessary to use a plurality of spindle motors for the plurality of disks (a spindle motor for each disk), contrasting with the case of the CAV disk in which a plurality of disks can be driven by a single spindle motor. This has been an obstacle in reducing the size of the apparatus or reducing the cost.